The present invention relates generally to testing of microelectronic packaging. More specifically, but without limitation thereto, the present invention relates to measuring degradation of microelectronic package interconnects due to current flow and elevated temperature, particularly due to electromigration.
An important issue in microelectronic packaging is reliability. Technologies for microelectronic packaging are developed not only to manufacture microelectronic packages at low cost, but also to ensure that the performance of the microelectronic packages will not deteriorate over their service life. One of the limiting factors of the service life of a microelectronic package is electromigration. Electromigration is the mass transport of atoms within metal interconnects of a microelectronic package due to momentum transfer between conduction band electrons and diffusing metal atoms. Since the invention of the first integrated circuits in the 1960""s, electromigration has been a major problem, and accelerated testing is still needed to determine whether a microelectronic package design will continue to function properly over its service life. Even accelerated testing may require more than a year, which substantially impacts marketing of new devices. Also, the costs of these tests may exceed $100,000 per year, excluding the investment in equipment. A faster method of testing microelectronic package interconnects is needed to fully exploit the market value of new devices.
The present invention advantageously addresses the needs above as well as other needs by providing an expedient method and apparatus for measuring electromigration.
In one embodiment, the invention may be characterized as a method for measuring electromigration that includes the steps of measuring a corresponding voltage increase across an interconnect as a function of time for a plurality of nonzero heating rates and calculating an interconnect integrity from the voltage increase.
In another embodiment, the invention may be characterized as an apparatus for measuring electromigration that includes a current source for generating a current through an interconnect; a controlled heat source coupled to the interconnect for heating the interconnect at a selected nonzero heating rate from a selected initial temperature; and a voltage measurement device coupled to the interconnect for measuring a voltage across the interconnect.
The features and advantages summarized above in addition to other aspects of the present invention will become more apparent from the description, presented in, conjunction with the following drawings.